JD755
Platinum Member
If you ever wondered what the inside of your mechanical drive tach/hour meter looks like, here it is. My tach needle began failing maybe ten years ago. At first it was jumpy and not always accurate. Then it would occasionally spin completely around. Then it got to where it would continually spin at high speed. Eventually the spinnng caused the needle to break off. I've owned the tractor for so long I know what the engine speed is without the tach so as long as the hour meter worked I was OK. Last week while using the tractor the hour meter started to become unreadable due to a grey powder rapidly building up on the numbers. The hour numbers had also stopped changing.
Since the meter was now junk I removed it and cut it open to analyze. The shaft behind the needle had broken and allowed the large cylinder with the tach spring to come apart and dump metal filings created by all that spinning down onto the hour meter. I suppose it could be some sort of graphite powder for damping the tach spring but maybe not. That also allowed the plastic gear at the back with the concave section that mated with the input spiral gear to lose contact and stop the hour meter gears from turning.
I bought a new meter at JD for $99.50 and installed it. Nice to have a tach again. It's been a long time since I had a working needle and this new one is smooth and very well damped. I'll just have to add the hours from the old meter to my log when I do maintenance.
Since the meter was now junk I removed it and cut it open to analyze. The shaft behind the needle had broken and allowed the large cylinder with the tach spring to come apart and dump metal filings created by all that spinning down onto the hour meter. I suppose it could be some sort of graphite powder for damping the tach spring but maybe not. That also allowed the plastic gear at the back with the concave section that mated with the input spiral gear to lose contact and stop the hour meter gears from turning.
I bought a new meter at JD for $99.50 and installed it. Nice to have a tach again. It's been a long time since I had a working needle and this new one is smooth and very well damped. I'll just have to add the hours from the old meter to my log when I do maintenance.
